Forced flow vapor generating unit



' April 12, 1966 P. H. KOCH FORCED FLOW VAPOR GENERATING UNIT Filed Aug. 7, 1963 l 4 Sheets-Sheet 1 INVENTOR Paul H. Koch A ril 12, 1966 P. H. KOCH FORCED FLOW VAPOR GENERATING UNIT 4 Sheets-Sheet 2 Filed Aug. 7. 1963 April 12, 1966 P. H. KOCH FORCED FLOW VAPOR GENERATING UNIT 4 Sheets-Sheet 5 Filed Aug. 7. 1963 A ril 12, 1966 P. H. KOCH 3,

FORCED FLOW VAPOR GENERATING UNIT Filed Aug. 7, 1963 4 Sheets-Sheet 4 United States Patent 3,245,385 FORCED FLOW VAPOR GENERATING UNIT Paul Henry Koch, Akron, Ohio, assignor to The Babcock & Wilcox Company, New York, N.Y., a corporation of New Jersey Filed Aug. 7, 1963, Ser. No. 300,536 9 Claims. (Cl. 122406) The present invention relates in general to the construction and operation of a forced flow fluid heating unit and more particularly to improvements in the construction and arrangement of fluid heating circuits especially adapted for use in a forced circulation once-through vapor generating and superheating unit and to contain a subcritical pressure vaporizable fluid.

The general object of the present invention is the provision of a fluid heating unit of the character described so constructed and arranged as to produce superheated vapor from a vaporizable fluid over a wide range of high pressures and temperatures without use of tempering equipment; to assure an optimum distribution of fluid to all fluid flow paths; to assure an optimum relation of fluid velocity within the tubes to heat input into the tube walls to effect adequate cooling of the tube walls to a safe temperature without imposing an excessive pressure drop in the fluid flow path; to provide a division of the fluid heating surface between the radiant and convection heated sections of the unit whereby generation of vapor is mainly accomplished in the furnace and a substantial part of the superheating of the fluid is carried out in the furnace; and to provide superheating and reheating of the fluid in tube banks disposed in parallel convection gas passes of the unit.

A further and more specific object of the invention is the provision of a special arrangement of fluid flow circuitry in the convection gas passes of a unit of the character described permitting by-passing of a portion of the fluid around such circuitry during operation in the upper part of the load range without overheating the tubes of the circuitry, thereby achieving a substantial reduction in pressure drop in the fluid flow path and a corresponding reduction in the feed pump power requirements and cost.

The various features of novelty which characterize my invention are pointed out with particularity in the claims annexed to and forming a part of the specification. For a better understanding of the invention, its operating advantages and specific objects attained by its use, reference should be had to the accompanying drawings and descriptive matter in which I have have illustrated and described a preferred embodiment of the invention.

Of the drawings:

FIG. 1 is a partly diagrammatic sectional elevation of a forced circulation once-through steam generating unit constructed and operable in accordance with the invention;

FIG. 2 is a partial sectional plan view taken along the line 2-2 of FIG. 1;

FIG. 3 is a partial sectional plan view taken along the line 33 of FIG. 1; and

FIG. 4 is a diagrammatic representation of the vaporizable fluid flow path within the steam generator of FIG. 1.

In the drawings the invention has been illustrated as embodied in a top-supported forced flow once-through steam generating unit intended for central station use. The particular unit illustrates a design for coal firing for a maximum continuous steam output of 3,900,000 lbs. steam per hour at a pressure of 2450 p.s.i.g. and a total temperature of 1053 F. at the superheater outlet, based on feed water being supplied at a temperature of 540 F and a maximum continuous steam output of 2,700,000 lbs. of steam per hour at a pressure of 495 p.s.i.g. and a total temperature of 1003" F. at the reheater outlet.

The main portions of the unit illustrated include an upright furnace chamber 10 of substantially rectangular cross-section defined by front wall 11, rear wall 12, side walls 13, and a roof 14 and having a gas output 16 at its upper end opening to a horizontally extending gas pass 17 of rectangular vertical cross-section formed by a floor 18 and extensions of the furnace roof 14 and side walls 13. Gas pass 17 communicates at its rear end with the upper end of an upright gas passage 19 of rectangular horizontal cross-section formed by a front wall 21, 'a rear wall 22, side walls 23 and a roof 24, and communicating at its discharge end with a pair of parallel flow gas passes 26, only one of which is shown, formed by insulation covered metallic casing. Furnace 10 is divided into three compartments 27A, 27B, 270 by a pair of vertical partition walls 28, each compartment opening at its upper end to the gas outlet 16, with upper portions of the walls 28 also dividing the gas inlet end of the pass 17 into parallel heating passes or sections 17A, 17B, 17C forming continuations of compartments 27A, 27B and 27C respectively. The lower portions of the front and rear walls of the furnace slope inwardly and downwardly and cooperate with the furnace side walls to form a hopper 31 and a rectangular throat passage 32 for discharging ash into an ash pit, not shown.

Gas passes 17A, 17B and 17C are occupied by a sec ondary superheater 30, while the remaining portion of the gas pass 17 is occupied in the direction of gas flQW by a secondary superheater 33 and a secondary reheater 34, both extending across the full width of the gas pass 17.

Upright gas passage 19 is divided into parallel heating gas passes or sections 36 and 37 by a vertical baflle 38, with the upper part of gas pass 36 being occupied by a second primary superheater 39B, the upper part of gas pass 37 by a primary reheater 41, and the lower part of both gas passes 36, 37 by a first primary superheater 39A disposed downstream gas flow-wise of superheater 39B and reheater 41. Proportioning of the gas flow between the passes 36, 37 is controlled by sets of dampers 43 and 44 at the discharge ends of the passes. Heating gases from the gas passes 36, 37 discharge into a common duct 30, then pass through a pair of ducts 35, only one of which is shown, to the parallel gas passes 26. Gas passes 26 are occupied by an economizer 42. After flowing through the passes 26 and over the economizer surface therein, the heating gases pass through an air heater 25, and thence to a stack.

The vapor generator is top-supported by structural steel members including upright members 46 and cross beams 47 from which hangers, not shown, support all walls.

The lower portion of the compartments 27A, 27B, and 27C of the furnace 10 are fired by horizontally extending burners 49 arranged to direct fuel and air in mixing relationship into the compartments through corresponding burner ports in the boundary walls of the furnace. The front and rear walls of the furnace each include five vertically spaced rows of burners, each row having three burners. Preheated air is supplied to the burners by a forced draft fan, not shown, which passes air under pressure through air heater 25 and suitable ductwork to a vertically extending windboX 51 enclosing the burners 49 and the lower portion of the front and rear boundary walls of the furnace 10.

Feedwater at a pressure of 3100 p.s.i.g. is supplied by feed pump, not shown, to economizer 42 wherein it is partially heated. Economizer 42 comprises two sections each occupying one of the gas passes 26 and including horizontally arranged multiple-looped nested return bend tubes disposed across the path of heating gas flow and connected at their opposite ends to lower inlet and upper outlet headers 52 and 53. From the outlet headers 53 the fluid flows through tubes 55, downcomers 54 and supply tubes 56 to the inlet headers for fluid heating tubes of the boundary and partition walls of the furnace.

Each of the upright boundary walls of the furance 10 is formed by a row of spaced vertically extending parallel tubes having their intertube spaces closed by metallic webs to provide a gas-tight construction and arranged in groups to form coplanar radiant heat absorbing tubular panels extending between horizontally arranged upper and lower headers. Thus front wall 11 has a row of tubes 57 having their intertube spaces closed by metallic webs to form tubular panels C extending to full height of the furnace between upper and lower headers 58 and 59; rear wall 12 has a row of tubes 61 having their intertube spaces closed by metallic webs to form tubular panels D extending between upper headers 62A, 62B and lower headers 63; and each side wall 13 has a row of tubes 64 extending the full height of the furnace and having their intertube spaces closed by metallic Webs to form four tubular panels A1 and three tubular panels A2, with one of the panels A2 occupying the central portion of the wall, the remaining panels A2 being situated at opposite extremes of the wall and the panels A1 being located intermediate the panels A2. Rear wall tubes 61 have their upper portions bent inwardly and upwardly to form a nose arch 71, and then rearwardly and upwardly to form a portion of the floor 18 of the gas pass 17, 'with some of the tubes 61 of each panel then continuing vertically upward at a position intermediate the secondary superheaters 30 and 33 for connection to the headers 62A and to form screen 72 and the remaining tubes 61 of each panel continuing rearwardly and upwardly to form the remainder of the floor 18 and then vertically upward for connection to the headers 62B and to form a part of a screen 73. Intermediate portions of some of the tubes of the front and rear walls of the furnace are suitably bent to form the openings or ports for the burners 49. The tubes of the panels A1 extend between upper and lower headers 66 and 67 and tubes of the panels A2 extend between upper and lower headers 68 and 69. Tubes '64 also line the portion of the side walls of the gas pass 17 opposite the secondary superheater 30 and ahead of screen tubes 72. Edge tubes of adjoining panels of the front and rear walls 11 and 12 and of adjoining panels A1 of the side walls 13 are rigidly united to each other along their furnace lengths by metallic webs disposed therebetween; while the edge tubes of adjoining panels A1 and A2 of the side walls are contiguous but not united to each other to permit relative longitudinal expansion movements between the panels A1 and A2.

Each of the partition walls 28 of the furnace 10 is formed by a row of vertically extending parallel tubes 74 arranged in groups to form coplanar radiant heat absorbing tubular panels B1 and B2 extending between upper and lower headers, with the tubes of each panel contacting each other along their lengths, and with the tubes of each panel B1 extending throughout the height of the furnace and the tubes of each panel B2 extending upwardly through the furnace from positions above and adjacent to the top of the hopper 31 to positions above the top of the furnace. Panels B2 are four in number for each partition wall and form the end portions thereof, while panels B1 are two in number and form the remaining intermediate portion, with the tubes of each panel B1 extending between horizontal upper and lower headers 76 and 77 and the tubes of panels B2 extending between horizontal upper and vertical lower headers 78 and 79. In each partition wall outermost panels B2 are spaced from the adjacent furnace boundary walls and panels B1 are spaced from each other to provide openings 81 for the flow of gases between the compartments 27A, 27B and 27C of the furnace.

The furnace boundary and partition wall fluid heating surface is so proportioned and arranged that the distribution of flow to all fluid flow paths is at an optimum; that the maximum temperature differential between adjacent connected tubes is below a predetermined critical limit, thereby maintaining differential expansions in the walls within safe limits; that fluid flow unbalances in the tubes are minimized; that the tube surfaces in different zones of heat intensity in the furance are suflicient in quantity to carry away the heat at a rate adequate to prevent overheating of the tubes; and that the tubes are of suflicient inside diameter along their lengths to provide adequate fluid circulation velocity. Accordingly, the fluid supply headers 67 for panels A1 of the side walls 13 and fluid supply headers for panels B1 of the partition walls 28 are connected to the downcomers 54 by the supply tubes 56. Each of the outlet headers 76 of the tube panels B1 of the partition walls 28 is connected and opens at one end to a horizontal header 82 above the furnace for flow of liquid thereto, while each of the outlet headers 66 of the tube panels A1 of the side Walls 13 are connected for series flow of liquid to the header 82 by tubular connectors 83. Header 82 extends parallel to the front wall 11 and constitutes the crossportion of a T-shaped header which has its leg portion 82A inclined upwardly at a slight angle to the horizontal and disposed in a vertical plane common to the centerline of the furnace. Header 82A is connected and opens to a horizontal header 84 disposed outwardly of and extending parallel to the front wall 11 and having its opposite ends connected and opening to downcomers 86. The liquids discharged from the tube panels A1 and B1 to the header 82 are mixed in passing through the headers 82, 82A and 84 so that the enthalpy, and thereby the temperature, will be substantially uniform upon discharge from the header 84. From the header 84 the liquid flows through downcomers 86 and supply tubes 87 to the inlet headers for the tube panels of the front wall 11 and rear wall 12, and tube panels A2 of the side walls 13. Thus water of substantially the same enthalpy and in a sub-cooled condition, that is, at a temperature below the saturation temperature corresponding to the pressure, is supplied in parallel flow relation from downcomers 86 to the headers 59, 63 and 69 by the supply tubes 87.

The fluid heating surfaces of the unit are proportioned and arranged so that throughout the operating range the portion of the heated fluid circuit in which the transition of the fluid from a water condition to a vapor-water condition will be located in the tube panels C and D of the front and rear walls 11 and 12 and in tube panels 2 of the side walls and the portion of the heated fluid circuit in which the transition of the fluid from a vaporwater condition to a vapor condition will be located in the relatively low temperature primary superheater 39A. Outlet headers 58, 62A, 62B, and 68 are connected by tubes 88 for series flow of the vapor-liquid mixtures generated in the front and rear wall tube panels and in the panels A2 of the side walls to a horizontal collection and distribution header 89 extending parallel to and outwardly of front wall 10 and connected for flow of fluid to a horizontal header 91 by a row of tubes 92 forming the roof of the furnace 10 and the gas passes 17 and 19, with header 91 being situated above the roof 24 of passage 19 and extending parallel to the rear wall 22 thereof.

The fluid supply system for the tubes lining the upright boundary and partition walls of the gas pass 19 and the upright side boundary walls of the portion of the gas pass 17 downstream gas flow-wise of screen tubes 72 is so constructed and arranged as to inhibit or prevent separation of the vapor from the water; to promote mixing of the fluid streams as they pass from the roof tubes 92 to the tubes of the gas passes 17 and 19, and thereby provide a substantially uniform fluid enthalpy upon discharge to the tubes of the gas passes 17 and 19; and to provide uniform distribution of the fluids to the tubes of the gas passes 17 and 19. Accordingly, the fluids collected in the header 91 are passed without further heating to the fluid supply headers for tubes of the gas passes 17 :and 19 by means of fluid mixing and distribution apparatus comprising an upright cylindrical vessel 93 of relatively large diameter closed at its opposite ends and extending along and outside of the wall 22 at the midpoint thereof. Vessel 93 has its upper end connected to header 91 by tubular connectors 94 leading radially into the vessel and a pair of downcomers 96 leading radially from its lower end to opposite sides of gas pass 19 and then downwardly along opposite sides of gas pass 19 to the level of the bottom of the passage 19, with supply tubes 97 connecting the lower ends of the downcomers 96 for parallel supply of fluid to the inlet headers for the tubes forming [boundary and partition walls of the gas passes 19 and 17.

Each of the upright boundary walls of the gas passage 19 and of the portion of the gas pass 17 downstream of superheater 30 is formed by a row of vertically extending spaced parallel tubes having their intertube spaces closed by metallic webs and arranged in groups to form coplanar tubular panels extending between a corresponding number of horizontal upper and lower headers. Thus front wall 21 has a row of tubes 98 forming tubular panels E extending between upper and lower headers 99 and 101; rear wall 22 has a row of tubes 102 forming tubular panels F extending between upper and lower headers 104 and 103; each side wall 23 has a row of tubes 106 forming tubular panels G extending between upper and lower headers 107 and 108; and the portion of each of the side walls of the gas pass downstream of superheater 30 is lined by a row of tubes 109 forming tubular panels H extending between upper and lower headers 111 and 112. Edge tubes of next adjacent panels H and A2 of the upright side boundary walls are rigidly united to each other by metallic webs disposed therebetween. These panels may be so united without creating undue thermal stresses since the fluid flowing through the respective panels is at saturation temperature. Baffie 38 is formed of a row of vertical tubes 113 arranged in groups to form coplanar tubular panels I extending between a corresponding number of upper and lower headers 114 and 116 and having their intertube spaces closed by metallic webs along their lengths from their points of connection to the headers 116 to a position immediately above the primary superheater 39B and their intertube spaces open along their remaining lengths up to the roof 24 to permit flow of gases from the gas pass 37 to the gas pass 36.

Inlet headers 101, 104, 108, 112, and 116, of the tube panels of the boundary and partition walls of the gas passes 17 and 19 are connected for parallel supply of fluid from the downcomers 96 by supply tubes 97; while outlet headers 99, 103, 107, 111 and 114 of the corresponding tube panels are connected by tubes 120 for series flow of vapor-liquid mixtures to a horizontally arranged transverse fluid collection and mixing header 117 disposed above gas pass 19 and wherein the vaporliquid mixtures are mixed so that the enthalpy, and thereby the temperature, will be substantially uniform upon discharge therefrom. Header 117 is connected for flow of the fluids thus mixed to a horizontally arranged transverse primary superheater inlet header 118 by Way of a pair of downcomers 119 and supply tubes 121, with header 118 being disposed immediately below and in the same vertical plane as baffle wall 38. Downcomers 119 are closed at their lower ends, extend horizontally from opposite ends of header 117 and then downwardly along opposite sides of gas pass 19 to a position below gas pass 19, and have their lower portions connected to header 118 by supply tubes 121.

Primary superheater 159A comprises two sections, one in gas pass 36 and the other in gas pass 37, each section including two groups of horizontally disposed multilooped tubes arranged in laterally spaced panels serially connected to define parallel flow paths for fluid flow be tween header 118 and a transverse outlet header 122 in counterflow heat transfer relation to the gases flowing through the corresponding gas pass, with outlet header 122 being disposed in gas pass 36 intermediate primary superheaters 39A and 39B. From the header 122 the partly superheated vapor passes to the second primary superheater 3913 which comprises two groups of horizontally disposed pendantly supported multilooped tubes arranged in laterally spaced panels with corresponding panels serially connected to define parallel flow paths for fluid flow between header 122 and a transverse outlet header 123- outside of rear wall 22. The additionally heated vapor then flows through a pair of downcomers 124, leading from intermediate positions along the length of header 123, and supply tubes 126 to the inlet headers 79 for the final primary vapor superheating tubes forming the end panels B2 of each partition wall 28. The vapor is further superheated in passing through panels B2 to outlet headers 78 each of which is connected and opens at one end to a horizontal vapor collection and distribution header 127 extending parallel to front wall 11 and disposed immediately above header 82. Vapor collected in header 127 is distributed to secondary superheater 30 by way of supply tubes 128.

Secondary superheater 30 comprises horizontally spaced pendantly supported radiant heat absorbing tube platens arranged in vertical planes in the direction of gas flow, with each platen having a multiplicity of nested return bend tubes connected at their inlet ends to a horizontal inlet header 129 and at their outlet ends to a horizontal outlet header 131, with the inlet headers 129 being connected to header 127 by the tubes 128 and with the outlet headers 131 on one side of the longitudinal centerline of gas pass 17 being connected and opening at one end to a horizontally arranged transverse common vapor collect-ion and distribution header 132 on the same side of the centerline and the outlet header 131 on the opposite side of the longitudinal centerline of gas pass 17 being connected and opening at one end to a horizontally arranged transverse common vapor collection and distribution header 133 on the opposite side of the centerline extending coaxially of the header 132.

Secondary superheater 33 comprises pendantly supported vertically disposed nested multiple-looped tubes arranged in laterally spaced panels to define parallel flow paths for vapor flow between a pair of coaxial horizontal inlet headers 134, 136 above gas pass 17 and a pair of horizontal outlet headers 137, 138 above gas pass 17, with the tubes being arranged so that the vapor flows in counterflow heat transfer relation with the gases flowing through gas pass 17 and then in parallel flow heat transfer relation. Headers 132 and 134 are disposed on the same side of the longitudinal centerline of gas pass 17, while headers 133 and 136 are disposed on the opposite side of the centerline with cross-over pipes 139 connecting header 132 for supply of vapor to header 136 and cross-over pipes 141 connecting header 133 for supply of vapor to header 134 to offset vapor temperature differences due to any maldistrihution of gas flow in gas pass 17. Headers 137 and 138 extend the full width of gas pass 17, with the tubes of alternate panels of secondary superheater 33 having their discharge ends connected to header 137 and the tubes of the remaining panels having their outlet ends connected to header 138. The vapor receives its final superheating in secondary superheater 33 and is discharged to headers 137 and 138 from which it passes through conduits 142 to the high pressure stage of a vapor turbine, not shown.

Primary reheater 41 comprises horizontally extending multiple-looped tubes arranged substantially similar to the tubes of the primary superheater 39A and in counterflow heat transfer relation with the heating gases. The tubes of reheater 41 have their lower ends connected to an inlet header 143 below gas pass 17 and their upper outlet ends connected by tube connectors 144 to the inlet ends of the tubes forming the secondary reheater 34, with inlet header 143 receiving partially expanded vapor from the turbine.

Secondary reheater 34 comprises vertically disposed nested return bend tubes arranged in laterally spaced panels and in counterflow heat transfer relation with the heating gases. Tubes of the reheater 34 receive partly reheated vapor from reheater 33 and discharge to a pair of transverse outlet headers 146, 147 above gas pass 19, with tubes of alternate panels having their outlet ends connected to header 146 and tubes of the remaining panels having their outlet ends connected to header 147. The finally reheated vapor passes from headers 146, 147 through conduits 148 to the turbine for final expansion.

The superheating and reheating surfaces are proportioned and arranged to provide the required final or outlet steam temperatures at full steam load. The proportions of the heating gases flowing through the parallel gas passes 36 and 37 are respectively increased and decreased by means of the dampers 43 and 44 as the rate of steam generation decreases to hold the reheater outlet steam temperature constant over a wide range of steam loads, while the final superheater outlet steam temperature is maintained constant by controlling the firing rate of the burners.

Combustion air and fuel are supplied through the burner ports to the lower portion of each of the compartments 27A, 27B, 27C. The resulting heating gases flow upwardly through compartments 27A, 27B, 27C; then flow horizontally through the parallel heating passes 17A, 17B, 17C and the remaining portion of gas pass 17, While successively contacting and passing over the tubes of the secondary superheater 30, secondary superheater 33, and secondary reheater 34; then divide into parallel streams, with one stream passing through gas pass 37 in contact with tubes of primary reheater 41 and primary superheater 39A, and the other stream passing through gas pass 36 in contact with tubes of primary superheaters 39A and 39B; then combine in the duct 30 and again divide into parallel streams for flow through the parallel gas passes 26 and over the economizer surface disposed therein.

With reference to FIG. 4, in operation up to a predetermined partial load high pressure fluid supplied by the 'feed pump passes through the economizer 42; then flows upwardly in parallel through the radiant heat absorbing tube panels A1 of the side walls 13 and panels B1 of the partition walls 28; then passes upwardly in parallel through the radiant heat absorbing tube panels A2 of the side walls 13, panels C of the front Wall 11 and panels D of the rear wall 12; then passes through the tubes forming the roof of the gas passes 17 and 19 and of the furnace then flows upwardly in parallel through the convection heat absorbing fluid heating tubes of the boundary and partition walls of gas pass 19 and of the side wall portions of the gas pass 17 downstream gas flow-wise of superheater then passes upwardly in parallel through the two sections of primary superheater 39A; then flows through primary superheater 39B; then passes upwardly in parallel through the radiant heat absorbing fluid heating tube panels B2 of partition walls 28; then successively passes through secondary vapor superheating tubes 30 and 33; and then flows to the high pressure stage of the turbine. Partially expanded steam from the turbine successively passes through primary vapor reheating tubes 41 and secondary vapor reheating tubes 34, from which it returns to the turbine for final expansion.

In accordance with the invention, during operation throughout the upper part of the load range of the vapor generator a portion of the fluid flowing through downcomers 96 is bypassed around the flow circuitry of the upright boundary and partition walls of gas passes 17 and 19 by means of conduits 149 connecting downcomers 96 and 119 on corresponding sides of gas pass 19 to each other, with each conduit being provided with a fluid control valve 151. Valves 151 always remain closed at low loads and during startups. When a predetermined partial load is reached valves 151 are opened manually or automatically with the controlling impulse coming from the load on the vapor generator. Bypass valves 151 may be operated in a number of ways. They may be operated to maintain the pressure drop of the fluid due to flow through the circuitry of gas passes 17 and 19 substantially constant from the predetermined partial load to full load. They may be operated in response to variations in load in such a manner as to have a given opening at a given load. They may also be completely opened at the predetermined partial load and maintained in this position to full load, in which case the pressure drop across the boundary and partition wall flow circuitry of the gas passes 17 and 19 immediately sharply decreases at the predetermined partial load and then gradually increases as the load increases. By any of these modes of valve operation, the pressure drop across the upright boundary and partition wall circuitry of gas passes 17 and 19 will be considerably less throughout the operative load range of the valves than the pressure drop that would exist without bypassing fluid around such circuitry, thereby providing a corresponding reduction in the feed pump power requirements and cost. While bypassing of fluid in the manner described will occasion an increase in the heat absorption per pound of fluid flowing through the boundary and partition wall flow circuitry of gas passes 17 and 19, the heat pickup per pound of fluid is so small, due to the fact that such circuitry is located in a relatively low gas temperature portion of the gas flow path, that fluid may be bypassed without overheating of the tubes of the circuitry.

By way of example, and not of limitation, in a commercial embodiment of the invention the valves 151 are designed to bypass a portion of the fluid flowing through downcomers 96 around the flow circuitry of the upright boundary and partition walls of gas passes 17 and 19 at loads above 64 percent of full load, with the valves being interlocked to open and close on load impulse. Valves 151 are fully opened at 64 percent load and maintained in this position as the load increases to full load. When the load drops, the valves 151 are maintained in their full open position until load reaches 69 percent of full load, at which point the valves are fully closed. Immediately before the valves 151 open on increasing load, the pressure drop across the upright boundary and partition wall circuitry is about 45 psi. When the valves 151 open the pressure drop immediately decreases to 12 psi. and then gradually increases as load increases to a full load value of 34 psi, which is about one-quarter of the pressure drop that would exist at full load without bypassing fluid around such circuitry.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A forced circulation vapor generator comprising walls forming a furnace chamber having a heating gas outlet, means for burning fuel in said furnace chamber, at least one of said walls including first and second radiant heat absorbing fluid heating tube panels, means forming a partition wall including first and second radiant heat absorbing fluid heating tube panels and dividing said furnace chamber into a plurality of gas flow compartments, means for flowing a vaporizable fluid of substantially the same enthalpy in parallel flow relation to and through the first tube panels of said one furnace and partition walls and means for interconnecting said fluid heating tube panels to provide a serial flow of fluid from said first tube panels successively through the second tube panel of said one furnace wall and the second tube pa'n'el of said partition wall.

2. A once-through forced circulation vapor generator comprising,walls forming an upright furnace chamber having a heating gas outlet, means for burning fuel in said furnace chamber, at least one of said walls including first and second radiant heat absorbing fluid heating tube panels, means forming a partition wall including first and second radiant heat absorbing fluid heating tube panels and dividing said furnace chamber into a plurality of gas flow compartments, means for flowing a vaporizable fluid of substantially the same enthalpy in parallel flow relation to and through the first tube panels of the partition wall and of said one furnace wall, and means for interconnecting said fluid heating tube panels to provide a serial flow of fluid from said first tube panels successively through the second tube panels of said one furnace wall and the second tube panels of said partition wall.

3. A once-through forced circulation vapor generator comprising walls forming an upright furnace chamber having a heating gas outlet, means for burning fuel in said furnace chamber, a pair of said walls including first and second radiant heat absorbing fluid heating tube panels, means forming a partition Wall including first and second radiant heat absorbing fluid heating tube panels and dividing said furnace chamber into a plurality of gas flow compartments, means for flowing a vaporizable fluid of substantially the same enthalpy in parallel flow relation to and through the first tube panels of the partition wall and of said pair of furnace walls, and means for interconnecting said fluid heating tube panels to provide a serial flow of fluid from said first tube panels successively through the second tube panels of said pair of furnace Walls and the second tube panels of said partition wall.

4. A once-through forced circulation vapor generator comprising walls including radiant heat absorbing fluid heating tube panels forming an upright furnace chamber having a heating gas outlet, means including convection heat absorbing fluid heating tube panels forming a gas pass serially connected to said gas outlet, means for buming fuel in said furnace chamber, a bank of vapor superheating tube in said gas pass in the path of gas flow leaving said furnace chamber, means forming a partition wall including first and second radiant heat absorbing upfiow fluid heating tube panels and dividing said furnace chamber into a plurality of gas flow compartments, a pair of said furnace walls including first and second upflow tube panels, means for supplying a vaporizable fluid of substantially the same enthalpy in parallel flow relation to the first tube panels of the partition wall and of said pair of furnace Walls, means interconnecting said fluid heating tube panels and vapor superheating tube to-provide a serial flow of fluid from said first tube panels successively through the second tube panels of said pair of furnace Walls, the convection heat absorbing fluid heating tube panels, the bank of vapor superheating tubes and the second tube panels of said partition wall.

5. A once-through forced circulation vapor generator comprising walls including upwardly extending radiant heat absorbing fluid heating tube panels forming an upright furnace chamber having a heating gas outlet at its upper end, means including convection heat absorbing fluid heating tube panels forming a horizontally extending gas pass opening at one end to said gas outlet, a bank of secondary vapor super-heating tubes positioned in said gas pass in the path of gas flow leaving said furnace chamber, means including convection heat absorbing fluid heating tube panels forming an upright gas passage laterally adjacent and opening to the opposite end of said gas pass, means including convection heat absorbing fluid heating tube panels dividing said upright gas passage into a pair of parallel flow gas sections, a bank of primary vapor superheating tubes positioned in said upright gas passage in one of the parallel gas flow section's thereof, a bank of primary vapor reheating tubes in said upright gas passage in the other of the parallel gas flow sections thereof, a bank of secondary vapor reheating tubes positioned in said gas pass and connected for serial flow of vapor from said bank of primary vapor reheating tubes, means forming a partition wall including first and second radiant heat absorbing fluid heating tube panels and dividing said furnace chamber into a plurality of intercommunicating gas flow compartments each opening at its upper end to said gas outlet, damper means arranged to proportion the heating gas flow through said parallel gas flow sections, means for burning fuel in the lower portion of each of the compartments of said furnace chamber, a pair of said furnace walls including first and second upfiow tube panels, means for supplying a vaporizable fluid of substantially the same enthalpy in parallel flow relation to the first tube panels of the partition wall and of said pair of furnace walls, means for interconnecting said fluid heating tube panels and vapor superheating tubes to provide a flow of fluid from said first tube panels to and in parallel through the second tube panels of said pair of furnace walls and the tube panels of the remaining upright walls of the furnace, and then successively through the convection heat absorbing fluid heating tube panels, the bank of primary vapor superheating tubes, the second tube panels of said partition wall, and the bank of secondary vapor superheating tubes.

6. In a forced circulation once-through vapor generating and superheating unit, walls forming a gas flow path, means supplying heating gases to said gas flow path, means forming a once-through fluid flow passage in said gas flow path arranged to receive a vaporizable fluid at one end and discharge superheated vapor at its opposite end, said passage comprising radiant heat absorbing fluid heating tubes disposed in a relatively high temperature portion of said gas flow path, a vapor superheating section, and a vapor generating section disposed in a relatively low temperature portion of said gas flow path and connected for series flow of fluid from said radiant heat absorbing fluid heating tubes and to said vapor superheating section, and means for bypassing a portion of the fluid inflow to said vapor generating section to said vapor superheating section.

7. In a forced circulation once-through vapor generating and superheating unit, walls forming a gas flow path, means supplying heating gases to said gas flow path, means forming a once-through fluid flow passage in said gas flow path arranged to receive a vaporizable fluid at one end and discharge superheated vapor at its opposite end, said passage comprising radiant heat absorbing fluid heating tubes disposed in a relatively high temperature portion of said gas flow path, a vapor superheating section, and a vapor generating section disposed in a relatively low temperature portion of said gas flow path and connected for series flow of fluid from said radiant heat absorbing fluid heating tubes and to said vapor superheating section, and means for bypassing a portion of the fluid inflow to said vapor generating section to said vapor superheating section, said last named means including a valve-controlled conduit interconnecting the fluid inflow side of said vapor generating section to the fluid inflow side of said vapor superheating section.

8. In a forced flow once-through vapor generating and superheating unit having walls defining a fuel-fired gas flow path, a once-through fluid flow path arranged to receive a vaporizable fluid at one end and discharge superheated vapor at its opposite end and comprising a vapor superheating section and a vapor generating section in a relatively low temperature portion of said gas flow path and connected for series flow of fluid to said vapor superheating section, and a valve-controlled conduit connecting the fluid inlet side of the vapor generating section to the fluid inlet side of the vapor superheating section, the meth- 0d of operating said unit which comprises passing all of the fluid entering said fluid flow path successively through said vapor generating and superheating sections throughout the lower part of the load range, and regulating the resistance of fluid flow through said vapor generating section throughout the upper part of the load range by bypassing a portion of the fluid inflow to the vapor generating section through said conduit to the fluid inlet side of the vapor superheating section.

9. In a forced flow once-through vapor generating and superheating unit having walls defining a fuel fired gas flow path, a once-through fluid flow path arranged to receive a vaporizable fluid at one end and discharge superheated vapor at its opposite end and comprising a vapor superheating section and a vapor generating section in a relatively low temperature portion of said gas flow path and connected for series flow of fluid to said vapor superheating section, and a valve-controlled conduit connecting the fluid inlet side of the vapor generating section to the fluid inlet side of the vapor superheating section, the method of operating said unit which comprises passing all of the fluid entering said fluid flow path successively through said vapor generating and superheating sections throughout the lower part of the load range, and regulating the resistance of fluid flow through said vapor generating section throughout the upper part of the load range by bypassing a portion of the fluid inflow to the vapor generating section through said conduit to the fluid inlet side of the vapor superheating section, and by proportioning the flow of fluid through said conduit and vapor generating section so that the quantity of fluid passing through said vapor generating section is sufiicient to assure that the fluid will he in a vapor-liquid condition upon discharge from said vapor generating section.

References Cited by the Examiner UNITED STATES PATENTS 2,781,746 2/1957 Arrnacost et a1 122240 2,879,750 3/1959 Engel 122-406 2,962,005 11/1960 Koch 122-478 FREDERICK L. MATTESON, JR., Primary Examiner.

KENNETH W. SPRAGUE, Examiner. 

1. A FORCED CIRCULATION VAPOR GENERATOR COMPRISING WALLS FORMING A FURNACE CHAMBER HAVING A HEATING GAS OUTLET, MEANS FOR BURNING FUEL IN SAID FURNACE CHAMBER, AT LEAST ONE OF SAID WALLS INCLUDING FIRST AND SECOND RADIANT HEAT ABSORBING FLUID HEATING TUBE PANELS, MEANS FORMING A PARTITION WALL INCLUDING FIRST AND SECOND RADIANT HEAT ABSORBING FLUID HEATING TUBE PANELS AND DIVIDING SAID FURNACE CHAMBER INTO A PLURALITY OF GAS FLOW COMPARTMENTS, MEANS FOR FLOWING A VAPORIZABLE FLUID OF SUBSTANTIALLY THE SAME ENTHALPY IN PARALLEL FLOW RELATION TO AND THROUGH THE FIRST TUBE PANELS OF SAID ONE FURNACE AND PARTITION WALLS AND MEANS FOR INTERCONNECTING SAID FLUID HEATING TUBE PANELS TO PROVIDE A SERIAL FLOW OF FLUID FROM SAID FIRST TUBE PANELS SUCCESSIVELY THROUGH THE SECOND TUBE PANEL OF SAID ONE FURNACE WALL AND THE SECOND TUBE PANEL OF SAID PARTITION WALL. 